<!DOCTYPE refentry PUBLIC "-//Davenport//DTD DocBook V3.0//EN" [

<!ENTITY seealso SYSTEM "@builddir@/see_also.sgml">

]>

<refentry>

<docinfo>

<date>@LXC_GENERATE_DATE@</date>

</docinfo>

<refmeta>

<refentrytitle>lxc</refentrytitle>

<manvolnum>7</manvolnum>

<refmiscinfo>

Version @LXC_MAJOR_VERSION@.@LXC_MINOR_VERSION@.@LXC_MICRO_VERSION@

</refmiscinfo>

</refmeta>

<refnamediv>

<refname>lxc</refname>

<refpurpose>

linux containers

</refpurpose>

</refnamediv>

<refsect1>

<title>Quick start</title>

<para>

You are in a hurry, and you don't want to read this man page. Ok,

without warranty, here are the commands to launch a shell inside

a container with a predefined configuration template, it may

work.

<command>

@BINDIR@/lxc-execute -n foo -f @SYSCONFDIR@/lxc/lxc-macvlan.conf /bin/bash

</command>

</para>

</refsect1>

<refsect1>

<title>Overview</title>

<para>

The container technology is actively being pushed into the

mainstream linux kernel. It provides the resource management

through the control groups aka process containers and resource

isolation through the namespaces.

</para>

<para>

The linux containers, <command>lxc</command>, aims to use these

new functionalities to provide an userspace container object

which provides full resource isolation and resource control for

an applications or a system.

</para>

<para>

The first objective of this project is to make the life easier

for the kernel developers involved in the containers project and

especially to continue working on the Checkpoint/Restart new

features. The <command>lxc</command> is small enough to easily

manage a container with simple command lines and complete enough

to be used for other purposes.

</para>

</refsect1>

<refsect1>

<title>Requirements</title>

<para>

The <command>lxc</command> relies on a set of functionalies

provided by the kernel which needs to be active. Depending of

the missing functionalities the <command>lxc</command> will

work with a restricted number of functionalities or will simply

fails.

</para>

<para>

The following list gives the kernel features to be enabled in

the kernel to have the full features container:

</para>

<programlisting>

* General setup

* Control Group support

-> Namespace cgroup subsystem

-> Freezer cgroup subsystem

-> Cpuset support

-> Simple CPU accounting cgroup subsystem

-> Resource counters

-> Memory resource controllers for Control Groups

* Group CPU scheduler

-> Basis for grouping tasks (Control Groups)

* Namespaces support

-> UTS namespace

-> IPC namespace

-> User namespace

-> Pid namespace

-> Network namespace

* Security options

-> File POSIX Capabilities

</programlisting>

<para>

For the moment the easiest way to have all the features in the

kernel is to use the git tree at:

<systemitem>

git://git.kernel.org/pub/scm/linux/kernel/git/daveh/linux-2.6-lxc.git

</systemitem>

But the kernel version >= 2.6.27 shipped with the distros, may

work with <command>lxc</command>, this one will have less

functionalities but enough to be interesting.

The planned kernel version which <command>lxc</command> should

be fully functionaly is 2.6.29.

</para>

<para>

Before using the <command>lxc</command>, your system should be

configured with the file capabilities, otherwise you will need

to run the <command>lxc</command> commands as root. The

control group should be mounted anywhere, eg:

<command>mount -t cgroup cgroup /cgroup</command>

</para>

</refsect1>

<refsect1>

<title>Functional specification</title>

<para>

A container is an object where the configuration is

persistent. The application will be launched inside this

container and it will use the configuration which was previously

created.

</para>

<para>How to run an application in a container ?</para>

<para>

Before running an application, you should know what are the

resources you want to isolate. The default configuration is to

isolate the pids, the sysv ipc and the mount points. If you want

to run a simple shell inside a container, a basic configuration

is needed, especially if you want to share the rootfs. If you

want to run an application like <command>sshd</command>, you

should provide a new network stack and a new hostname. If you

want to avoid conflicts with some files

eg. <filename>/var/run/httpd.pid</filename>, you should

remount <filename>/var/run</filename> with an empty

directory. If you want to avoid the conflicts in all the cases,

you can specify a rootfs for the container. The rootfs can be a

directory tree, previously bind mounted with the initial rootfs,

so you can still use your distro but with your

own <filename>/etc</filename> and <filename>/home</filename>

</para>

<para>

Here is an example of directory tree

for <command>sshd</command>:

<programlisting>

[root@lxc sshd]$ tree -d rootfs

rootfs

|-- bin

|-- dev

| |-- pts

| `-- shm

| `-- network

|-- etc

| `-- ssh

|-- lib

|-- proc

|-- root

|-- sbin

|-- sys

|-- usr

`-- var

|-- empty

| `-- sshd

|-- lib

| `-- empty

| `-- sshd

`-- run

`-- sshd

</programlisting>

and the mount points file associated with it:

<programlisting>

[root@lxc sshd]$ cat fstab

/lib /home/root/sshd/rootfs/lib none ro,bind 0 0

/bin /home/root/sshd/rootfs/bin none ro,bind 0 0

/usr /home/root/sshd/rootfs/usr none ro,bind 0 0

/sbin /home/root/sshd/rootfs/sbin none ro,bind 0 0

</programlisting>

</para>

<para>How to run a system in a container ?</para>

<para>Running a system inside a container is paradoxically easier

than running an application. Why ? Because you don't have to care

about the resources to be isolated, everything need to be isolated

except <filename>/dev</filename> which needs to be remounted in

the container rootfs, the other resources are specified as being

isolated but without configuration because the container will set

them up. eg. the ipv4 address will be setup by the system

container init scripts. Here is an example of the mount points

file:

<programlisting>

[root@lxc debian]$ cat fstab

/dev /home/root/debian/rootfs/dev none bind 0 0

/dev/pts /home/root/debian/rootfs/dev/pts none bind 0 0

</programlisting>

More information can be added to the container to facilitate the

configuration. For example, make accessible from the container

the resolv.conf file belonging to the host.

<programlisting>

/etc/resolv.conf /home/root/debian/rootfs/etc/resolv.conf none bind 0 0

</programlisting>

</para>

<refsect2>

<title>Container life cycle</title>

<para>

When the container is created, it contains the configuration

information. When a process is launched, the container will be

starting and running. When the last process running inside the

container exits, the container is stopped.

</para>

<para>

In case of failure when the container is initialized, it will

pass through the aborting state.

</para>

<programlisting>

---------

| STOPPED |<---------------

--------- |

| |

start |

| |

V |

---------- |

| STARTING |--error- |

---------- | |

| | |

V V |

--------- ---------- |

| RUNNING | | ABORTING | |

--------- ---------- |

| | |

no process | |

| | |

V | |

---------- | |

| STOPPING |<------- |

---------- |

| |

---------------------

</programlisting>

</refsect2>

<refsect2>

<title>Configuration</title>

<para>The container is configured through a configuration

file, the format of the configuration file is described in

<citerefentry>

<refentrytitle><filename>lxc.conf</filename></refentrytitle>

<manvolnum>5</manvolnum>

</citerefentry>

</para>

</refsect2>

<refsect2>

<title>Creating / Destroying the containers</title>

<para>

The container is created via the <command>lxc-create</command>

command. It takes a container name as parameter and an

optional configuration file. The name is used by the different

commands to refer to this

container. The <command>lxc-destroy</command> command will

destroy the container object.

<programlisting>

lxc-create -n foo

lxc-destroy -n foo

</programlisting>

</para>

</refsect2>

<refsect2>

<title>Starting / Stopping a container</title>

<para>When the container has been created, it is ready to run an

application / system. When the application has to be destroyed

the container can be stopped, that will kill all the processes

of the container.</para>

<para>

Running an application inside a container is not exactly the

same thing as running a system. For this reason, there is two

commands to run an application into a container:

<programlisting>

lxc-execute -n foo [-f config] /bin/bash

lxc-start -n foo [/bin/bash]

</programlisting>

</para>

<para>

<command>lxc-execute</command> command will run the

specified command into a container but it will mount /proc

and autocreate/autodestroy the container if it does not

exist. It will furthermore create an intermediate

process, <command>lxc-init</command>, which is in charge to

launch the specified command, that allows to support daemons

in the container. In other words, in the

container <command>lxc-init</command> has the pid 1 and the

first process of the application has the pid 2.

</para>

<para>

<command>lxc-start</command> command will run the specified

command into the container doing nothing else than using the

configuration specified by <command>lxc-create</command>.

The pid of the first process is 1. If no command is

specified <command>lxc-start</command> will

run <filename>/sbin/init</filename>.

</para>

<para>

To summarize, <command>lxc-execute</command> is for running

an application and <command>lxc-start</command> is for

running a system.

</para>

<para>

If the application is no longer responding, inaccessible or is

not able to finish by itself, a

wild <command>lxc-stop</command> command will kill all the

processes in the container without pity.

<programlisting>

lxc-stop -n foo

</programlisting>

</para>

</refsect2>

<refsect2>

<title>Connect to an available tty</title>

<para>

If the container is configured with the ttys, it is possible

to access it through them. It is up to the container to

provide a set of available tty to be used by the following

command. When the tty is lost, it is possible to reconnect it

without login again.

<programlisting>

lxc-console -n foo -t 3

</programlisting>

</para>

</refsect2>

<refsect2>

<title>Freeze / Unfreeze a container</title>

<para>

Sometime, it is useful to stop all the processes belonging to

a container, eg. for job scheduling. The commands:

<programlisting>

lxc-freeze -n foo

</programlisting>

will put all the processes in an uninteruptible state and

<programlisting>

lxc-unfreeze -n foo

</programlisting>

will resume all the tasks.

</para>

<para>

This feature is enabled if the cgroup freezer is enabled in the

kernel.

</para>

</refsect2>

<refsect2>

<title>Getting information about the container</title>

<para>When there are a lot of containers, it is hard to follow

what has been created or destroyed, what is running or what are

the pids running into a specific container. For this reason, the

following commands give this information:

<programlisting>

lxc-ls

lxc-ps -n foo

lxc-info -n foo

</programlisting>

</para>

<para>

<command>lxc-ls</command> lists the containers of the

system. The command is a script built on top

of <command>ls</command>, so it accepts the options of the ls

commands, eg:

<programlisting>

lxc-ls -C1

</programlisting>

will display the containers list in one column or:

<programlisting>

lxc-ls -l

</programlisting>

will display the containers list and their permissions.

</para>

<para>

<command>lxc-ps</command> will display the pids for a specific

container. Like <command>lxc-ls</command>, <command>lxc-ps</command>

is built on top of <command>ps</command> and accepts the same

options, eg:

<programlisting>

lxc-ps -n foo --forest

</programlisting>

will display the process hierarchy for the container 'foo'.

</para>

<para>

<command>lxc-info</command> gives informations for a specific

container, at present time, only the state of the container is

displayed.

</para>

<para>

Here is an example on how the combination of these commands

allow to list all the containers and retrieve their state.

<programlisting>

for i in $(lxc-ls -1); do

lxc-info -n $i

done

</programlisting>

And displaying all the pids of all the containers:

<programlisting>

for i in $(lxc-ls -1); do

lxc-ps -n $i --forest

done

</programlisting>

</para>

<para>

<command>lxc-netstat</command> display network information for

a specific container. This command is built on top of

the <command>netstat</command> command and will accept its

options

</para>

<para>

The following command will display the socket informations for

the container 'foo'.

<programlisting>

lxc-netstat -n foo -tano

</programlisting>

</para>

</refsect2>

<refsect2>

<title>Monitoring the containers</title>

<para>It is sometime useful to track the states of a container,

for example to monitor it or just to wait for a specific

state in a script.

</para>

<para>

<command>lxc-monitor</command> command will monitor one or

several containers. The parameter of this command accept a

regular expression for example:

<programlisting>

lxc-monitor -n "foo|bar"

</programlisting>

will monitor the states of containers named 'foo' and 'bar', and:

<programlisting>

lxc-monitor -n ".*"

</programlisting>

will monitor all the containers.

</para>

<para>

For a container 'foo' starting, doing some work and exiting,

the output will be in the form:

<programlisting>

'foo' changed state to [STARTING]

'foo' changed state to [RUNNING]

'foo' changed state to [STOPPING]

'foo' changed state to [STOPPED]

</programlisting>

</para>

<para>

<command>lxc-wait</command> command will wait for a specific

state change and exit. This is useful for scripting to

synchronize the launch of a container or the end. The

parameter is an ORed combination of different states. The

following example shows how to wait for a container if he went

to the background.

<programlisting>

# launch lxc-wait in background

lxc-wait -n foo -s STOPPED &

LXC_WAIT_PID=$!

# this command goes in background

lxc-execute -n foo mydaemon &

# block until the lxc-wait exits

# and lxc-wait exits when the container

# is STOPPED

wait $LXC_WAIT_PID

echo "'foo' is finished"

</programlisting>

</para>

</refsect2>

<refsect2>

<title>Setting the control group for a container</title>

<para>The container is tied with the control groups, when a

container is started a control group is created and associated

with it. The control group properties can be read and modified

when the container is running by using the lxc-cgroup command.

</para>

<para>

<command>lxc-cgroup</command> command is used to set or get a

control group subsystem which is associated with a

container. The subsystem name is handled by the user, the

command won't do any syntax checking on the subsystem name, if

the subsystem name does not exists, the command will fail.

</para>

<para>

<programlisting>

lxc-cgroup -n foo cpuset.cpus

</programlisting>

will display the content of this subsystem.

<programlisting>

lxc-cgroup -n foo cpu.shares 512

</programlisting>

will set the subsystem to the specified value.

</para>

</refsect2>

</refsect1>

<refsect1>

<title>Bugs</title>

<para>The <command>lxc</command> is still in development, so the

command syntax and the API can change. The version 1.0.0 will be

the frozen version.</para>

</refsect1>

&seealso;

<refsect1>

<title>Author</title>

<para>Daniel Lezcano <email>daniel.lezcano@free.fr</email></para>

</refsect1>

</refentry>